This invention relates to titanium alloy parts which are subjected to high surface stresses in use. More specifically, this invention relates to a method of treatment of such parts during their manufacture which will have the result of increased fatigue life. The invention is useful in the manufacture of titanium alloy parts in which high stresses are developed in and adjacent to the surface. Typical parts and devices which develop such high surface stresses in use are connecting rods, springs and spring devices, spring wire, torque rods, drive shafts, and the like. Such parts are increasingly being manufactured from titanium alloys because of the weight savings.
During the manufacturing of titanium alloy springs, such parts are subjected to aging or other heat treatment. Due to the reactive nature of titanium alloys, such treatments result in surface oxidation. In the present state of the art, the titanium parts are subjected to a nitric acid pickling process to descale the oxidation products. However, it has been found that the acid pickling process is detrimental to the part surface conditions as it preferentially attacks the alpha particles at the grain boundaries in beta-titanium alloys, such as Ti-13V-11Cr-3Al and Ti-8Mo-8V-2Fv-3Al. The attacked grain boundaries act as notches and fatigue cracks initiate at these sites. Also, during the pickling process, hydrogen is picked up, which causes hydrogen embrittlement or hydride formation in certain titanium alloys.